Transformer tap changing



Oct. 27, 1936. o. P. M cARTY 20,147

TRANSFOIRHERITAP CHANGING MECHANISM OriginaLFiled Nov. 29, 19:53

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UNITED STATES PATENT OFFICE mnsroma TAP cmixomo nmcnnmsm Orin P. M00111!- Plttsfleld, Mas... llllnor to General Electric Co New York pany. a corporation of Original No. 2,004,998, dated June 18, 1935, Serial No. 700,239, November 29, 1933. Application for reissue October 30, 1935, Serial No. 47,430

Claims. (01. 171-119) The invention will be more fully explained in r the following description taken in connection with the accompanying drawing which shows diagrammatically an .auto transformer provided with voltage ratio adjusting means arranged in accordance with the invention.

The transformer l0 indicated in the drawing is connected between a high voltage circuit II and a low voltage circuit II, the transformer winding having a common section B and a series section l4. The series winding section I4 is provided with taps l5 distributed along it and connected to the fixed contacts i6 and ll of two switches it and I! respectively; The switch l8 has two movable contacts and 2| fixed to a commonshaft but angularly displaced and insulated from each other. The switch i9 has two similarly arranged insulated and angularly displaced movable contacts 22 and 23.

One side of the high voltage circuit II is con-- nected directly to the movablecontact 2| and through an impedance 24 and a fuse 24 or other -circuit interrupting device to the movable contact 20 of the switch It. Any form of impedance 24 desired may be used and it is shown in the drawing as asimple, non-inductive resistance. One side of the low voltage circuit l2 and the inner end of the common winding section I! are connected directly to the movable contact 23 and through a resistance 25 and a fuse 25 or other circuit interrupting device to the movable contact 22 of the switch i9. The two movable contacts of each of the switches II and i9 are normally positioned on the same fixed contact It or l1 respectively. It will be apparent that any desired number of turns of the series winding section l4 may be connected by means of the switches II and It in either direction in series with the common winding section i3. Thus, up to the maximum number of turns in the series winding section l4, any number of turns desired maybe connected in either direction in series with the common winding section it. With the switches in the positions shownin the drawing the entire series winding section i4 is connected in series with the common winding section It.

The two sets of movablecontacts of the two switches I8 and I! are operated by the two gears 28 and 21 of a double Geneva gear driven through a worm 28 and pinion 29 by a reversible motor 30. The driving element I of the double Genevai gear has a single driving pin 32 so arranged that one half revolution of the driving element 3| will rotate one or the other .of the gear wheels 26 and 21 to change the voltage ratio of the transformer.

The coil 33 of a contact-making voltmeter 34 'is connected to an auxiliary winding 35 inductively coupled to the common winding section I! of the transformer it. The movable contact 38 of the voltmeter is biased by a spring 31 to hold it in neutral position under the normal desired voltage conditions in the low voltage circuit I! which will be considered as the secondary or load circuit, the circuit being the primary circuit.

Now, if the voltage of the circuit i2 drops, the

movable contact of the voltmeter 84 will be pulled against the back contact 38 and close a circuit which may be traced from one terminal of the winding 35 through the back contact 38 of the voltmeter, the winding 39 of a relay 40 and back to the other terminal of the winding 35.

' This will cause the relay 40 to close two sets of contacts 4| and 42. Closing the contacts 42 completes a circuit which may be traced from one terminal of the winding 35 through a conductor 43, the contacts 42, one side of the motor 30 and back through a conductor 44 to the other terminal of the winding 35. Current from the winding 45 will then start the motor in a direction to operate the switches I8 and I! to raise the voltage of the circuit II.

A drum contactor 4I fixed to the shaft of the driving member ll of the Geneva gear has a narrow section of insulation upon which normally rest three brushes 41, 4t and. The remainder of the drum contactor 45 is conductive. As soon as the motor starts, the three brushes 41, 48 and cycle of operation of the switches even though the voltmeter contacts I6 and 38 should breakthe circuit before completion of the cycle. The con tactor 45 rotates with the driving member 3| of the Geneva gear so that the insulating section 48 oi the contactor is brought under the contacts 41, 45 and 49 at the end of each operating cycle of the Geneva gear and therefore of the switches I8 and I9. This breaks the holding circuit through the contacts 4| and returns control of the relay 3! to the contact making volt meter 34. If the change in position of the switch has adjusted the voltage of the transformer to its normal value. then the contacts 36 and 3B of the contact making volt meter will open, the relay 39 will be released to open its contacts 42 and the motor will stop. If, the transformer voltage is still below its normal value, then the contacts 38 and IQ of the volt meter 34 will still be closed and maintain current in the relay 3! to start another switch operating a cycle. Thus the switches i8 and I! cannot stop in any intermediate position but must complete each operating cycle after it is once started.

If the voltage of the circuit 2 rises, the movable contact 36 of the voltmeter 34 will be moved against the front contact 50 of the voltmeter to close a circuit which may be traced from one ter minal of the winding 35 through the contacts 36 and IQ of the voltmeter, the winding 5| of a relay 52 and the conductor 44 back to the other terminal of the winding 35. This will cause the two sets of contacts 52 and 54 of the relay 52 to close with the result that the switches l8 and I9 will be operated ina direction to raise the-voltage of the circuit l2, the contacts 54 controlling the motor 30 and the contacts 53 controlling a hold- -ing circuit through the winding ii of the relay 52 to assure the completion of each cycle of operation of the switches l8 and It. This operation is similar to that which has been described in connection with the relay 40 for raising the voltage of the circuit i2 and it will be easily understood without further description.

The two movable contacts of each of the switches l8 and I! are moved very quickly from one fixed contact to the next by means of the Geneva gear drive. Referring to the switch ll, its two movable'contacts 2Il-and 2| are normally positioned on the same fixed contact it. After a slight motion, however, the movable contact 2| leaves this fixed contact I! and until it reaches the next contact IS an of the primary current will fiow through the resistance 24 with its fuse= 24' and the movable contact 20. After the movable contact 2| reaches the next fixed contact It, the resistance 24 and its fuse 24' will be bridged across'the two contacts l5. and will carry a circulating current due to the voltage between the transformer taps l5 to which the two contacts I. are connected. An instant later the movable contact 20 will leave the first contact Ii and then all of the primary current of the transformer may fiow directly through the movable contact 2|.

Under normal conditions there is very little or no current fiowing through the resistance 24 and its fuse 24' except for a very brief instant while the movable contact 2| of the switch is moving between two fixed contacts ii. In case of accidental breakage or faulty operation of some part of the switch operating mechanism, however, it is possible that the switch might stop with its movable contact 2| between two fixed contacts i6. Under this condition the resistance 24, if not protected, would have to be large enough to carry the full primary current indefinitely or its destruction would be almost certain. This would mean that the primary circuit and therefore the supply of electrical energy to the load circuit would be interrupted. It is usually highly important that the supply'of energy to a commercial load on a transformer be reliable and not subject to any interruption not absolutely necessary. It would, however, be very expensive to provide the resistance 24' of such capacity as to carry the entire primary current indefinitely. In accordance with the invention, the resistance 24 is provided with a fuse 24 or other circuit interrupter and a cutout 55 is connected across the terminals of the resistance and fuse. out may be of any suitable construction but it is indicated in the drawing as including two conductive plates58 connected to the two terminals of the series connected resistance and fuse and separated by an insulating film 51. which will break down under a predetermined voltage across the cutout and thus short circuit the resistance and fuse. The cutout 55 is designed to withstand the voltage across the resistance and fuse during the very brief instant while the resistance is carrying full primary current under normal switch operating conditions. If this full primary current continues to fiow'through the resistance, however, due to faulty operation of the switch, the fuse 24' will blow as a result of the PR heating effect of the current and protect the resistance. The film 51 will then instantly break down and permit the current to flow and the load circuit to be supplied with energy without interruption.

A cutout 58 is similarly connected across the resistance 25 and fuse 25' or other circuit interrupter associated with the movable contacts 22 and 23 of the switch IS. The purposeand function of this cutout 58 and fuse 25' are the same as has been already described in connection with the cutout 55 and fuse 24' and will be clearly understood without further description.

The inventionprovides an inexpensive but effective arrangement for assuring continuity of service in'electrieal circuits having impedances subject to brief or intermittent loads.

The invention has been explained by describing and illustrating its application in connection with a particular form of transformer and control mechanism but it will be obvious that it may be otherwise applied without departing from the spirit of the' invention and the scope of the appended claims.

What I claim as new, and desire to secure by Letters Patent of the United States, is:-

1. The combination with a transformer winding provided with taps, of a switch having fixed contacts connected to said taps and two contacts insulated from each other and movable along said fixed contacts, means for moving said movable This 'cut- 2. The combination with a transformer wind- ;ing provided with taps, of a switch having fixed contacts connected to said tape and two angular 15 ly displaced contacts insulated from each other and movable along said fixed contacts, an impedanceandacircuitinterrupterconnectedinseries between said movable contacts, and a normally open cutout connected in parallel with said impedance and interrupter, said circuit interrupter being responsive after a predetermined interval of time to open the circuit through said switch, whereby substantially full circuit voltage is impressed across said cutout, and said cutout being responsive to said voltage to close said circuit.

3. The combination with a transformer winding provided withtaps. of a switch having fixed contacts connected to said taps and two contacts insulated from each other and movable along said fixed contacts, means for moving said movable contacts alternately from one fixed contact to another, an impedance and a circuit interrupter connected in series between said movable contacts andhaving substantially smaller current carrying capacity than that due to maximum normal transformer load, and a normally open cutout connected in parallel with said impedance and interrupter, whereby substantially full circuit voltage is impressed upon. said cutout upon operation of said circuit interrupter, said cutout being responsive to said circuit voltage to break down and short circuit the two movable contacts.

4. In an alternating current circuit, an impedance, a circuit interrupting means in series with said impedance, and a normally open cutout connected in parallel with said impedance and circuit interrupting means, said circuit interrupting means being responsive after a predetermined interval of time to open said circuit, whereby substantially full circuit voltage is impressed across said cutout, and said cutout being responsive to said voltage to close said circuit.

5. The combination with an impedance fortransformer tap changer under load, of protective means for short circuiting the current path through said impedance, said protective means being actuated in response to the PR heating efi'ect of a current greater than a predetermined amount fiowing through said impedance for longer than a given time.

6. The combination with an impedance for carrying the main current during the operation of a transformer tap changer under load, of protective means for short circuiting the current path through said impedance, said protective means being controlled by a fusible element actuated in response to theI'R heating efiect of a current greater than a predetermined amount fiowing through said impedance for longer than a given time.

7. In combination, a transformer having a windingprovidedwithtapaaswitchhavingfixed contacts connected to said taps and having a movable contact for selectively said fixedcontactssoastovarytheratioofsaid transformer under load, automatic meam for operating said movable contact, said means being subject to stopping said movable contact between fixed contacts, an impedance connected so as to carry theswitch current when said movable contact is moving between fixed contacts, and

means for protecting said impedance if said movable contact stops between fixed contacts, said protective means acting to maintain a conducting path for said switch current.

8. In combination, a transformer having a winding provided with taps, a switch having fixed contacts connected to said taps and having a movable contact for selectively engaging said fixedcontacts so as to vary the ratio of said transformer under load, automatic means for operating said movable contact, said means being subject to stopping said movable contact between fixed contacts, an impedance connected so as to carry the switch current when said movable contact is moving between fixed contacts, and means for short circuiting the current path through said impedance when said movable contact stops between fixed contacts.

9. In combination, a transformer having a I winding provided with taps, a switch having fixed contacts connected to said taps and having a movable contact for selectively engaging said fixed contacts so as to vary the ratio of .said transformer, an impedance connected so as to carry the switch current when said movable contact is moving between fixed contacts, normally nonconductlng means for bypassing said impedance, and means connected in series with said impedance for controlling the operation of said b means.

10. In combination, an electric circuit, a transformer connected in said circuit and having a winding provided with taps, a switchhaving fixed contacts connected to said taps and having a movable contact for selectively engaging said fixed contacts so as to vary the ratio of said transformer, means responsive to variations in the voltage of said circuit from a predetermined value for controlling the operation of said movable contact, an impedance connected so as to carry the current when said movable contact is moving between fixed contacts, normally nonconductive means for b said impedance,

,and fusible means connected in series with said impedance for controlling the operation of said b means. I

CRIN P. McCAR'rY. 

